Push the lap button to stop a lap at the Y (the screen will show basic info for lap 1). You have to push it while moving and before the unit auto pauses (if you've set auto pause) for lap to work.
Push the start/stop button to stop recording (the screen should say "Timer Stopped"). You can then leave the unit on or turn it off.
When you leave the Y push the start/stop button to start recording again (the screen should say "Timer Started").
Push the start/stop button when you get home (the screen will show "Timer Stopped").
When you look at the info you'll have 1 lap to the Y and 1 lap to home. If you don't push the lap button when you get to the Y, it'll show as 1 lap.